Subscription television system



March l, 1966 M. G. PAwLl-:Y ETAL 3,238,297

suBscRIPTIoN TELEVISION SYSTEM 7 Sheets-Sheet 1 Original Filed June 8,195] j ATTORNEY March 1, 1966 M. G. PAWLEY ETAL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM 7 Sheets-Sheet 2 Original Filed June 8,195] IHA NNN

March l, 1966 M G, PAWLEY ETAL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM Original Filed June 8, 195] '7Sheets-Sheet 3 j: i; INVENTOILS /Zyf zyley Jaz/'05% facial,

/T m'ver 2Q BY p ATTORNEY March 1, 1966 M. G. PAWLEY ET AL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM Grgnal Filed June 8. 195] 7 Sheets-Sheet4.

INVENTORS '{y/'az LPWZay JwM'ac/.sj BY p ATTORNEY E |i|is L March l,1966 M. G. PAWLEY ETAL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM Original Filed June 8, 195] '7Sheets-Sheet 5 March l, 1966 M. G. PAwLEY ETAL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM 7 Sheets-Sheet 6 Original F'iled June 8,195] mm nQ/k INVENTORS TTORNEY March 1, 1966 M. G. PAWLEY ETAL 3,238,297

SUBSCRIPTION TELEVISION SYSTEM Original Filed June 8. 195] '7Sheets-'Sheet 7 INVENTORS BY Y p ATTORNEY United States Patent O3,238,297 SUBSCRIPTION TELEVISION SYSTEM Myron G. Pawley, Riverside, andJacob M. Sacks, Corona, Calif., assignors to Zenith Radio Corporation, acorporation of Delaware Original application .lune 8, 1951, Ser. No.230,618, now Patent No. 2,816,156, dated Dec. 10, 1957. Divided and thisapplication Dec. 5, 1957, Ser. No. 700,854 3 Claims. (Cl. 17822) Thepresent invention relates generally to image transmission or televisionsystems of the subscriber type. More particularly, the system of thepresent invention provides a transmitting station which broadcasts animage which cannot be received by the conventional receiver or the imagereceived will be so distorted or jittered that it cannot be viewednormally. The subscribers receiving stations, however, are each providedwith a coder unit which corresponds to a similar coder unit at thetransmitting station. By means of these coder units the pictures orimages received by the subscribers are corrected for distortion orjitter and appear normal. This is a divisional application of copendingapplication Serial No. 230,618, filed June 8, 1951, and issued December10, 1957, as Patent 2,816,156, and assigned to the present assignee.

Broadly, the coder units at the transmitter and at the subscribersreceivers can be adjusted to vary the scanning code to effect variablyabnormal scanning from program to program. For any one program, allcoder units produce the same scanning code. Alternately, the coder unitscan be arranged `to effect reversal in the polarity of the video signal,or other abnormal switching or operation. If desired, the same coderunits can be arranged for simultaneously controlling the electronicswitching of soundscrambling devices. In this manner the audio as wellas Ithe video signals received with the conventional television set aredistorted unless the distortion is removed by suitable decodingapparatus at the subscribers television set,

In order to provide for varying the scanning code from program toprogram, each coder unit at -the transmitter and at each subscribersreceiver is provided with adjustable devices or Variable setting means,such as a series of two-position toggle switches, which need to be setfor each program in order to have the coder unit produce the selectedscanning code which is being produced by the transmitter coder unit.While all coder units are thereby set to produce the same scanning code,it will be seen that the setting of each series of two-position toggleswitches is individual to each receiving station for any selected code.Thus each receiver coder unit has a key code or individual combinationwhich prescribes the setting of the adjustable devices or two-positionswitches to correspond with any given transmitter scanning code.

Under the present system, therefore, when a subscriber wishes to receivea program he communicates with the transmitting station by telephone, bymail, or in any desirable manner and he obtains the key code individualto his receiver for the specific program. This key code or switchsetting combination advises him how to set the switches on his coderunit, and when he so sets the switches, the coder unit will produce thesame scanning code as that produced at the transmitting station. Thesubscribers receiver will then be in phase with the transmitter and willproperly reproduce the image being televised. The key code of any onesubscriber for a specific program will differ from the corresponding keycodes of all or substantially al1 other subscribers in the area.

Another feature of the present system is that the coder unit employedgenerates a binary code which is represented by a repeated group of ONor OFF pulses.

"ice

A further feature of the present invention is that all the coder unitsin the entire system, including the transmitting station and allsubscribers stations, are controlled by the vertical synchronizing pulsewhich is generated by the transmitter and broadcast with the videosignal. The controlling operations are performed during the verticalretracing time when the screen is blanked out.

A still further feature of the present system is that a reducedfrequency resetting pulse or signal is derived from the verticalsynchronizing signal and employed for maintaining all coder unitsproperly energized and operating in synchronism. For this purpose thecomposite video and synchronizing signal broadcast by the transmitteralso contains this code system synchronizing pulse or reset signal whichis employed at the receiver in the same manner as at the transmitter,namely, to energize and operate the coder unit in phase with itscounterpart at the transmitter.

It is an object of thepresent invention to provide a new and improvedsubscription television arrangement that may be employed in either atransmitter to effect coding or in a receiver to achieve decoding.

A subscription television system, constructed in accordance with oneaspect of the invention, comprises a secrecy device having a pluralityof distinct operating conditions each of which establishes a differentoperating mode in the system. A control mechanism is coupled to thesecrecy device and has plurality of stable operating conditions, each ofwhich is effective to establish the secrecy device in an assigned one ofits operating conditions. A plurality of input circuits are provided forthe control mechanism and each of these selectively energiza'ble tooperate the control mechanism to a different assigned one of itsoperating conditions. The system has a rst signal source including anadjustable codedetermining switching apparatus for developing a rstseries of code signal pulses having an irregular time spacing determinedat least in part by the instanteous adjustment of said code-jdeterminingswitching apparatus and also a second signal source for developing asecond series of code signal pulses, the rst and second series of pulsescollectively representing a code schedule. Mean coupled to the firstsignal source and to one of the input circuits are provided forutilizing the code signal pulses of the first series to selectivelyenergize the one input circuit. Finally, the subscription televisionsystem includes means coupled to second signal source'and to another oneof the input circuits for utilizing the code signal pulses of the secondseries to selectively energize the other input circuit, whereby thecontrol mechanism is operated between its operating conditions inaccordance with the code schedule.

In accordance with another aspect of the invention, a subscriptiontelevision system is provided which receives a scrambled picturetransmission wherein picture signals are transmitted in one of aplurality of different modes during different time periods which occurat a ra-te sufficient to render an unauthorized receiver displayunintelligible and wherein signals are transmitted representing theoperation of commutation` means at the transmitter. The receivercomprises means for resolving the different modes of the picturesignals, and means including commutation means coupled to the resolvingmeans for determining from time to time the mode resolved in theresolving means. Means are provided for detecting the transmittedsignals and coupled with the commutation means for maintainingsynchronization of the receiver commutaltion means with correspondingcommutation means at the transmitter. The receiver also includeschangeable matrix means connected between the mode resolution means andthe receiver commutation means for determining the mode to be resolvedfor given states of the commutation means.

The organization and manner of operation of the present invention andfurther objects and advantages thereof may be best understood byreference 4to the following specification and the accompanying drawings,it being understood that these serve to illustrate an embodiment of theinvention, and that variations thereof falling within the scope of theappended claims will be apparent to persons skilled in the art.

In the drawings:

FIGURE 1 is a block diagram of a transmitting station embodying theinvention;

FIGURE 2 is a block diagram of a subscribers station embodying theinvention;

FIGURE 3 is a schematic showing of a binary coder employing a rectitiernetwork and its driver unit;

FIGURE 4 is a schematic showing of a two-position electronic switch;

FIGURE 5 is a schematic showing of a four-position electronic switch;

FIGURE 6 is a diagrammatic showing of a reset pulse double coder;

FIGURE 7 is a diagrammatic illustration of a reset pulse separator;

FIGURE 8 is a diagrammatic showing of one form of a magnetic binarycoder;

FIGURE 9 is a diagrammatic showing of another form of a magnetic binarycoder; and

FIGURE 10 illustrates the broadcast waveform.

In FIGURE l the transmitting ysystem illustrated provides that thehorizontal scanning in the camera should recurrently step out of time orout of phase with the horizontaly synchronizing signal as broadcast.This recurrent time or phase shift is varied in accordance with a codeof ON or OFF pulses generated by the coder unit. It will be understood,however, that this represents only one type of jitter or distortion andthe other types of jitter -or distortion or abnormal operation may beeffected by means of the present invention, such as a coded reversal inpolarity of the video signal, or reversal in the direction of scanning.

In the system shown in FIGURE 1, picture signal generating tube 10 maybe of any desirable type which delivers the video signal to videoamplifier 11. The amplified video signals are then transmitted to mixer12 which receives the blanking, horizontal synchronizing, and thevertical synchronizing signals from their corresponding generators 13,14 and 15. The composite signal is then passed to modulator 16 whichmodulates R.F. amplifier 1S which in turn supplies the signal to theantenna. The oscillator 17 supplies its output to RF. amplifier 18.

The scanning of the image in the camera tube 10 is controlled byvertical scanning generator 19 and horizontal scanning generator 20which provide scanning power to their respective yokes 21 and 22.

The parts thus far described are the usual elements of a conventionaltelevision transmitter and need not be described with any furtherdetail. In the conventional television transmitter the horizontalsynchronizing generator is connected directly to the horizontal sweep orscanning generator for the camera.

In the present system, however, delay line 23 is interposed between thehorizontal synchronizing signal generator and the horizontal sweepgenerator at the transmitter. In the absence of the delay line thehorizontal scanning would be in step with or in phase with thehorizontal synchronizing signal. The interposition of the delay linebetween the synchronizing signal generator and the horizontal sweepgenerator provides for a time or phase shift between the horizontalscanning at the camera and the horizontal synchronizing signal asbroadcast.

The present invention further provides that this shift should bevariable in accordance with a code. For this purpose the delay line isprovided with two outgoing leads 24 and 25. One of these leads, such as24, may by-pass the delay line, whereas the other lead 25 is connectedto the output of the delay line. Electronic switch or control mechanism26 operates to connectl either lead 24 or lead 25 to the horizontalsweep generator of the camera through wire 27.

Merely for the purpose of simplifying the present diagram, the delayline is shown with the two outgoing leads described above. It will beunderstood, however, that, if desired, the delay line may includeseveral delay sections with a corresponding number of outgoing leadlines and a multi-postion electronic switch may then operate to vary theamount of delay as desired in accordance with the code.

The operation of the electronic switch is controlled by coder 28 whichwill be discussed more in detail in a later portion of thisspecification. At this point, however, it should be understood thatcoder unit 28 controls the operation of control mechanism or switch 26in accordance with a code which may lbe varied as desired by the propersetting of an adjustable code-determining switching apparatus in theform of a plurality of toggle switches.

Broadly, the coder unit is an apparatus which receives regularly spacedpulses and then converts such regularly spaced pulses into a repeatedbinary code which is represented by irregularly spaced ON or OFF pulses,derived by the proper setting of a plurality of toggle switches. TheseON or OFF pulses are delivered to the electronic switch or controlmechanism which thereby serves to vary the connection of the delay line23 to the horizontal scanning generator.

While the coder unit may be operated by any desired source of regularlyspaced pulses, it is advantageous to operate it by the verticalsynchronizing pulses which customarily recur at a rate of 60 per second.For this purpose the vertical synchronizing generator 15 at thetransmitter is connected to electronic driver 29 of the coder.

The coder employed in the present system receives the regularly spacedvertical synchronizing pulses, which recur conventionally at a rate of60 per second, and as a result of its operation it delivers at itsoutput a repeated cycle of ON or OFF pulses representing binary digits,these pulses being in phase with the vertical synchronizing pulses. Inorder to maintain the operation of the coder and to eliminate allnecessity for its adjustment during its operation, it is desirable toprovide the coding system with a pulse which coincides with the first ofeach group of the code. Thus if the code provides for a group of 8 ON orOFF pulses, it is desirable to provide the coding system with a singlepulse for every eighth vertical synchronizing pulse, the same, ofcourse, to be in phase with the synchronizing pulses. This cycling pulsewill be referred to as the reset or code system synchronizing pulse.

The reset pulse, it will be understood, serves at the transmittingstation, and, as will appear later, also at the subscribers receivingstations to synchronize the several components in each code system. Forthis purpose vertical synchronizing generator 15, which, as has beendescribed, delivers its output to vertical scanning generator 19 forconventional vertical scanning, also delivers its output to reset pulsegenerator 30. Reset pulse generator 30 may be any suitable conventionalfrequency divider and operates to receive the vertical synchronizingpulses at the rate of 60 per second and deliver pulses at a reducedfrequency, as for example one for every eight vertical synchronizingpulses, to cycler 31, shown in FIG- URE 8. The frequency of the pulsesdelivered by the reset pulse generator is determined by the number ofpulses in each code group. When, for example, the code group has eightON or OFF pulses the reset pulse generator will be designed to deliverone reset pulse f or every eight vertical synchronizing pulses. Thereset pulses are delivered by generator 30 to reset pulse cycler ordistributor 31 which distributes the reset pulses to the severalcomponents of the code system in order to maintain them in phase. Cycler31 is therefore connected for this purpose to driver 29 which operatesor drives the binary coder 28, and to the control mechanism 26 whichserves to switch the delay line 23 into the connection from horizontalsynchronizing generator 14 to horizontal scanning generator 20.

The vertical synchronizing generator which provides the conventionalvertical synchronizing pulses for the entire television system, and ashas been stated above, provides pulses to the reset pulse generator,also supplies its pulses to driver 29 of coder unit 28.

As will appear later, the present invention provides for the use of anysuitable type of binary coder such as a counter chain which generatesrepeated groups of ON or OFF pulses which constitute a code, and moreparticularly the present invention may employ one of two types of binarycoder which will be described in detail later but which will be herenamed as a magnetic binary coder and a rectifier network binary coder.The block 2S is intended to illustrate both types of coders. In theblock diagram in FIGURE 1 binary coder 28 is shown connected by dottedlines to cycler 31 and to vertical pulse generator 15. This is to showthat these two connections are alternatives and one or the other isemployed, depending upon whether one or the other type of binary coderis employed at 28. When the magnetic binary coder is employed at 28 itis connected to cycler 31 and is thus energized once for each group ofcode pulses by the reset pulse; when the diode network is employed asthe coder at 28 then it is connected to vertical pulse generator 15 andthe network operates to transmit the vertical pulse to the electronicswitch or control mechanism 26 for an ON pulse, or to shunt the pulse toground to produce an OFF pulse in the code. This action will bedescribed in more detail later.

It may now be stated, by way of recapitulating what has thus far beendescribed, that in the television system of the present invention, thetransmitting station employs a binary coder, which may be magnetic, ormay be a diode network or any other suitable type, its essential featurebeing that it can deliver to the electronic switch a repeated codeconsisting of ON or OFF pulses. The electronic switch in turn isoperated thereby to connect varied portions of a delay line between thehorizontal synchronizing generator and the horizontal sweep generator.This coding system is under the control of the vertical synchronizingpulses and the several components thereof are maintained in synchronismor in phase by a reset pulse which is derived from the verticalsynchornizing pulse by a frequency divider.

What has been said above with reference to the code system of thetransmitting station is also applicable to the code system of eachlsubscribers station, and each s-ubscribers station also contains a codesystem which is substantially identical with the code system as thus fardescribed. The code systems of the subscribers stations are maintainedin synchronism with the code system of the transmitting station by meansof the reset pulse which is broadcast as part of the composite video andsynchronizing signal transmitted or broadcast by the conventionaltelevision transmitting station. For this purpose the reset pulsesgenerated at 36 are delivered to reset pulse coder 32 which shapes orcodes the reset pulse so that the same can be readily separated from theother synchronizing pulses at the receiving station. The specific typeof pulse coder employed here and which will be described more in detailin a later portion of the specification, substitutes a coded doublepulse for the single reset pulse, and this double -coded pulse isdelivered to mixer 12 and transmitted with the conventionalsynchronizing4 pulses and video signal.

In FIGURE l, the dashed line divides the block diagram into two parts,in which the part that includes the picture yconverter 10 and theelements 11 to 12, inclusive, constitute a conventional transmitter,while the other part of FIGURE l shows in block vdiagram the codingsystem including the components 23-32, inclusive7 the diagram alsoshowing the manner in which the coding system is related to theconventional transmitter.

Before considering the receiver, it is best to consider the codingsystem employed at the transmitter in more detail. Many parts of thecoding system are well known or are found in the literature relating toelectronics and, therefore, will not be described in full detail,

An understanding of the present coding system necessitates rst anunderstanding of the coder unit 28. It has already been stated that thecoder unit employed in the present system receives a sequence ofregularly spaced pulses and delivers a repeated series of ON or OFFpulses. The preferred form of the coder unit may be briefly referred toas a diode binary coder unit and is shown in schematic form in FIGURE 3.

The theory of operation of the general type of circuit used in thiscoder is presented in a paper entitled, Rectiiier Networks forMultiposition Switching, by D. R. Brown and N. Rochester, Proceedings ofthe I.R.E. February l949, pp. 139-147, and the same is embodied herewithand made a part of the present specification by reference.

For simplicity, the particular arrangement illustrated in the drawingsand to be described generates successive groups of eight binary digitsrepresented by ON or OFF pulses, but it is clear that the coder unit mayreadily be enlarged or extended so as to produce groups of any requirednumber of binary digits with optional switch arrangements for setting upthe scanning code in corresponding with a key code for the switches.

The diode binary coder shown in FIGURE 3 comprises a network of eighthorizontal leads and six vertical leads which are interconnected by theunidirectional diodes 36 as shown. Each horizontal lead has atwo-position switch 37 connecting the same to the input A through asuitable resistor. At the output end the horizontal leads are eachconnected to the output C through the diodes 38. Switches 37collectively constitute an adjustable codedetermining switchingapparatus.

This network is indicated in FIGURES 1 and 2 by block 2S. FIGURE 3 alsoshows the driver (shown in FIGURES l and 2 in block 29) for the binarycoder, which consists here of a bank of three tubes forming a scale ofeight system and three gated switch tubes 33, 34 and 35.

In this system the switching tubes 33, 34 and 35 remain energized andthe current in each tube alternates from one plate circuit to the otherrepeatedly. In tube 33 this alternation or switching takes place at eachvertical pulse; tube 34 switches every two vertical pulses and tube 35switches for every fourth vertical pulse.

By means therefore of this operation of the switch tubes 33, 34 and 35half the vertical lines in the network are grounded and the other halfare ungrounded at any particular instant. The ydiodes or unidirectionalelements 36 are disposed to connect the vertical ylines with thehorizontal lines so that at all times only one horizontal line isungrounded and a pulse received by the network at A will be delivered atits output C via the ungrounded horizontal line, if it is connected tothe input A by a closed switch. The operation of the switch tubes shiftsthe ground in a manner that at every pulse a different horizontal lineis ungrounded and in the course of eight vertical pulses each horizontalline becomes ungrounded for the duration of the pulse. Thus for everygroup of eight vertical synchronizing pulses, each horizontal line inthe network transmits an ON or an OFF pulse, depending on whether it isconnected to or disconnected from the input A. The switches 37 in thehorizontal lines therefore determine the code, and by varying the ON orOFF position of the eight switches the code generated by the coder isdetermined.

It will now be understood that in this system the rectifier network typeof binary coder generates a code and that the code generated isdetermined by the key code which gives the positions of the switches 37.

In operation, therefore, the vertical synchronizing pulses are deliveredfrom generator 15 (FIGURE 1) to' the rectifier network at input A and toinput B of the scale-of-eight switching system. As these input pulses.progress the switch tubes 33, 34 and 35 are activated by thescale-of-eight circuit and the diodes connected to the: switch tubeplates are correspondingly grounded. lnspection of the diagram of FIGURE3 will show that, coincident with any particular input pulse, all of thehorizontal wires in the diagram except one will be effectively groundedthrough diodes. This particular input pulse will pass through to outputterminal C only if the switch S in the ungrounded horizontal wire isclosed. Similarly, with succeeding input pulses, only one horizontalwire at a time is ungrounded and the pulse on that lead will pass tooutput terminal C only if the switch in that lead is closed. Thecumulative effect of this action in the eight binary digit coder shownis to generate a sequence of groups of eight binary digits, representedby repeating groups of eight ON or OFF pulses, appearing at terminal Cwhen a uniform succession of pulses is fed to coder input terminal A andto scale-of-eight driver circuit input B. When all switches are closedno pulses are deleted from the output, but when any particular switch Sis opened the correspondingly-numbered pulse in the group of eight willbe deleted from the output at the terminal C. Thus, at terminal C aseries of code signal pulses is developed having an irregular timespacing determined at least in part by the instantaneous adjustment ofcode-determined switching apparatus 37. In practice, a slight delay isinterposed in the pulses arriving at the input terminal A in order toallow sufficient time for the scale-of-eight switching action to becomeeffective before the pulses appear at the input terminal A.

The purpose of the rectifier elements 38 in FIGURE 3 is to insure thatthe pulses appearing on any horizontal lead will not pass to the otherhorizontal leads.

The rectifier elements used in the diode binary coder may be germaniumdiodes, selenium elements, or any -suitable unidirectional elements.

The previously mentioned code system synchronizing pulse, or resetpulse, is applied to the diode coder at input D in order to synchronizethe coder operation with the corresponding coder operation at thesubscribers receiving stations. A source of these pulses is available atthe transmitter and at all subscribers stations. The reset pulse ispreferably generated by frequency division from the verticalsynchronizing pulse at the transmitter and transmitted in the sameenvelope with the video and conventional synchronizing pulses. Thesereset pulses perform the same service in the transmitter and in allreceivers. Broadly, the reset pulses maintain all coder units energizedin synchronism.

In the present system the reset pulses are generated at the transmitterby the frequency divider shown at 30 in FIGURE 1. The frequency of thereset pulse is determined by the number of binary digits or ON or OFFpulses in each code group generated by the coder unit 28, it beingdesirable to have one reset pulse for each group of code pulses. Thuswhen the coder unit generates an eight-digit code, it is desirable tohave one reset Apulse for every eight code digits. Since the code digitsare syn- -chronized with the vertical synchronizing pulses, there willbe generated by the frequency divider one reset pulse for every eightvertical synchronizing pulses. Such pulsefrequency dividers are commonin the art and will not be described in detail here. See Waveforms,byChance, Hughes, MacNichol, Sayre and Williams, Radiation LaboratorySeries, vol. 19, chapter 17, McGraw-Hill Book Co., this being embodiedhere by reference.

As thus far described, the diode coder unit 28 shown in schematic formin FIGURE 3 may be set by proper adjustment of the switches S to delivera predetermined code group of eight binary digits or ON or OFF pulses,the unit being triggered by the vertical synchronizing pulses andrecycled at the group rate by the code system synchronizing pulse.

The groups of ON or OFF pulses constitute a jittering or phasing codefor abnormal scanning of the picture converter 10. Alternately, thesecoded pulse groups can be vused to effect irregular reversing of thepolarity of the video signal, irregular direction of scanning or otherabnormal switching.

The binary-coded pulse groups may also be used simultaneously forirregular switching of sound-scrambling devices to make the soundunintelligible as received on conventional television receivers unlesscorrected by correspondingly coded switching at the subscribersreceivers.

It should be pointed out that although for simplicity a coder unit ishere described for the generation of groups of eight binary digits, thecoder unit may readily be eX- tended for the generation of say 16 or 32binary-digit groups. In the case of the l6digit coder, there would beover 65,000 scanning or switching codes available corresponding todifferent settings of the coding switches. With the 32-digit coder therewould be over four billion possible code settings.

The binary coder effects irregular triggering of the electronic switchor control mechanism connecting alternately delayed and undelayedhorizontal synchronizing -pulses to scanning generator 20 for pictureconverter 10. The sequence of pulses from the binary coder triggers, inan irregular but adjustable fashion, the two-position electronic switchshown in FIGURE 4. Each successive pulse from the coder unit is appliedto both of the input circuits of the electronic switch and thus causesV4a and V411 to conduct alternately; this action alternately turns onthe switch tubes V3a and V3I). In other words, electronic switch orcontrol mechanism 26 has two operating conditions and pulses aresimultaneously applied to both of its two input circuits to effectoperation thereof from :its instantaneous condition, whichever one thatmay be, to its alternate condition. When either of these switch tubesconducts it effectively grounds the diode which is connected to itsplate and prevents the pulse from the delay line from passing that diodeto output terminal E. The electronic switch therefore alternatelyconnects the terminals D0 and D1 of the delay line to output terminal E.The horizontal synchronizing pulses at the transmitter are fed to thedelay line and the pulses appearing at terminal D0 are undelayed,whereas those appearing at terminal D1 are delayed by a fixed amount. Toinsure synchronous operation between the transmitter and the receivers,reset pulses from cycler 3l are applied to only one of the inputcircuits of electronic switch 26 to actuate it to a predete-rminedreference condition from time to time if it is not already establishedin that reference condition.

Since the delay line shown in FIGURE 4 and the circuitry of andincluding tubes V3a land V317 collectively cooperate to either delay thehorizontal synchronizing pulses before application to scanning generator20 or to translate them with no appreciable delay, such apparatusconstitutes a secrecy device, labeled 100, having a plurality,specifically two, of distinct operating conditions each of whichestablishes a different operating mode in the system, namely a differenttime relationship between the video and radiated horizontalsynchronizing components. Tubes Vita and V4b and their associatedcircuitry, which together form electronic switch 26, may also beconsidered a control mechanism having a plurality of stable operatingconditions, specifically two, each effective to establish secrecy devicein an assigned one of its two operating conditions. Each one of tubesV4a and V4b has an input circuit for controlling its conductivecondition and thus it may be stated that there are a plurality of inputcircuits for control mechanism 26, each selectively energizable tooperate control mechanism 26 to a ditferent assigned one of itsoperating conditions. Binary coder 28 and driver 29 constitute a iirstsignal source including adjustable code-determining switching apparatus37 for developing (at output terminal C) a irst series of code signalpulses having an irregular time spacing determined in part by theinstantaneous adjustment of code-deterrnining switching apparatus 37 andcycler 31 may be considered a second signal source for developing asecond series of code signal pulses, the first and second series ofpulses collectively representing a code schedule.

The coupling `circuitry between binary coder 28 and the input circuit oftube V4b` may be considered means coupled to the first signal source andto one of the input circuits of control mechanism 26 for utilizing thecode signal pulses of the lirst series to selectively energ-ize thatinput circuit. Finally, the circuitry between cycler 31 and the inputcircuit of tube V40 constitutes means coupled to the second signalsource and to another one of the input circuits for utilizing the codesignal pulses of the second series to selectively energize the otherinput circuit, Consequently, the control mechanism is operated betweenits twooperating conditions in accordance with the code schedulecollectively represented by the pulses from binary coder and driver 2S,29 and from cycler 31.

If desired, Ia multi-sectional 'delay line may be used to provide formore than two operating modes. FIGURE 5 shows a three-section delay lineand a four-position electronic switch or control mechanism. Itsoperation will be .apparent from what has appeared above in connectionwith the description of FIGURES 3 and 4. In the operation of theelectronic switches, the delivery of an ON pulse by the coder will causethe switch to operate so as to provide a new path for the horizontalsynchronizing pulse to the output -at E. An OFF .pulse delivered by thecoder permits the switch to remain in its previous position. The pulsesappearing at output terminal E are therefore jittered in time at anirregular rate established by the setting of the coder switches at thetnansmitter. These jittered pulses are passed to the sweep generatingcircuit in the camera at the transmitter.

By inverting the position of the `switches 37 in `the diode binary coderor by varying the order of the switches, the number of individual coderunits at the subscribers receivers becomes enormous and it becomes.practically impossible fora group of friends to rewire the coder unitsso that they m-ay all operate ou the same key code.

In order for the previously mentio-ned reset pulse to be identied andseparated at the receiver it must be coded in some manner at thetransmitter. FIGURE 6 is a schematic diagram showing reset pulses coder32. This circuit receives the single pulse generated by frequencydivider 30 .and delivers the double-coded reset pulse to mixer 12. Thistype of circuit is similar to one shown in Waveforms, by Chance, Hughes,MacNichol, Sayre, and Williams; Radiation Laboratory Series, vol. 19, p.367; McGraw-Hill Book Company. Alternately, the reset pulse may be codeddifferently by methods well known to the art. See, for example,Electronic Time Measurements, by Chance, Hulsizer, MacNichol, IandWilliams, Radiation Laboratory Series, vol. 20, p. 432; McGraw- HillBook Company, this being embodied herein by reference.

Referring to FIGURE 6, del-ay line L1 is matched by a resistor R2 at itsinput end, is short-circuited at the other end, Iand has a tap Dmicroseconds from the input end. A negative pulse applied to the inputcauses tube V1b to conduit by its action on the cathode, giving anegative pulse on its plate. The negative input pulse also travelsthrough the delay line, is reflected as a positive puise, and (2L-D)microseconds later arrives at po-int D, where L represents the totaldelay of the line and D -together with the video and synchronizingsignals.

-retrace time between fields.

represents the displacement of tap D from the input end'. The delayedpositive pulse on the grid results in a second negative pulse on theplate of Vllb. The single negative input pulse is therefore coded into adouble pulse with spacing of (2L-D) microseconds. Tube Vla serves as aphase-inverter to supply positive double-coded pulses to mixer 12. Aswill be explained later, this doublecoded reset pulse may be decoded atthe receiver by a similar circuit. The reset pulse is used at thereceiver to synchronize the actions of the binary coder and electronicswitch units with corresponding lunits at the transmiter.

In the present system the binary coder at the transmitting stationserves to insert a coded delay into the horizontal scanning and at thereceiving station a similar coder inserts the same coded delay in thehorizontal scanning with the result that the -image received by thesubscribers station is undistorted. While the code is generated at eachsubscribers station, the code system is maintained in phase with thecode system of the transmitting station by the reset pulse which istransmitted The reset pulse is preferably transmit-ted during thevertical During such retrace, equilizing pulses land the verticalsynchronizing pulse are transmitted as shown in the approximate waveform shown in FIGURE l0. The double coded reset pulse is included in thegroup of signals that .are transmitted during the retrace time, thisreset pulse occurring there only at every eighth retrace' time, when thenumber of digits in the code is eight.

FIGURE 2 is a block diagram of a receiving system embodying the presentinvention and, insofar as the items there shown correspond to theequivalent or the same items in FIGURE 1, the same reference charactersare employed. In this system the signal is received and amplified byradio frequency amplifier 60 whose output is delivered to mixer ordetector 61 which also receives the output of local oscillator 62. Thesound signals are delivered by this detector in the direction indicatedby the arrow and the legend sound The video and its accompanyingsynchronizing signals are delivered by mixer 61 to amplifier 63 whichdelivers its output to second detector 64 which in Aturn delivers itsoutput to video ampliiier 65. The video -signals are delivered byampliiier 65 to D.C. restorer 66 and the video 'signals are deliveredthereby to picture converter 10.

The composite synchronizing signal is delivered by amplifier 65 tocomposite synchronizing amplifier and separator 67. The separatordelivers the vertical synchronizing signal to vertical synchronizingpulse oscillator 15 which in turn delivers its output to verticalscanning generator 19 which controls vertical scanning yoke 21.Separator `67 delivers the horizontal synchronizing component tohorizontal synchronizing oscillator 14 which in the 4conventionalreceiver delivers its output to horizontal scanning generator 20, thelatter being connected to horizontal scanning yoke 22.

The system as thus far described constitutes a conventional televisionreceiving system.

In addition to the system as thus described, the present receivingsystem also contains a coder system which in its essential respects issubstantially identical with the coder system at the transmittingstation as described above. This system serves to code the horizontalsweep at the receiver in a manner identical with the coding of thecamera horizontal sweep at the transmitting station, and as a resultthereof the jittered video signal, which would be unintelligible orimpossible to view normally by means of a conventional receiver, becomesconverted into a normal picture at the subscribers receiving station.

Alternatively, the coder unit at the receiver may effect irregularswitching in synchronism with corresponding switching of polarity ofvideo signals, direction of scanning, or other abnormal switching at thetransmitter in l1 order to derive an undistcrted television image at thesubscribers receiver. The same coder unit at the receiver maysimultaneously be used to unscramble the sound distorted by the coderunit at the transmitter.

In addition to receiving the jittered video signal, the subscriberstation also receives a code system synchronizing pulse which for thesake of brevity is referred to as the reset pulse. Synchronizing pulseseparator 67 delivers the vertical synchronizing pulse and thedoublecoded reset pulse to reset pulse separator 71 to be describedlater. From this composite signal reset pulse separator 71 delivers tocycler 31 the reset pulse in substantially the form as generated byfrequency divider 30 of the transmitting station. The reset pulseseparator thus constitutes a source of reset pulses which serve the samefunctions at the receiver as they served at the transmitter.

Cycler 31 shown in FIGURE 2 delivers the reset pulses to driver 29 andto electronic switch or control mechanism 26 in order to synchronizethese units with the corresponding units at the transmitter.

As in FIGURE l, the two dot and dash lines in FIG- URE 2 connected tocoder unit 28 indicate the connection of the two dilferent types ofcoder units that may be employed. If the coder unit employs therectifier network described, then it receives vertical synchronizingpulses by one of the dashed lines and it is not connected to cycler 31.If, however, the magnetic .binary coder is employed then it is energizedby the reset pulse delivered by cycler 31 and the coder unit is notconnected to Vertical oscillator 15.

Horizontal synchronizing generator 14, instead of being connecteddirectly to horizontal scanning generator 20, is connected to delay line23 which has two output lines supplying zero-delay and xed-delay pulses.Electronic switch or control mechanism 26, Controlled by binary coderunit 28, connects, in an irregular fashion, either one or the other ofthe output terminals of the delay line with the horizontal scanninggenerator.

It will now be understood that with the switches of coder unit 28 at thesubscriber station set so as to generate the same binary coded group ofpulses or coding pattern of signals as that produced by the coder unitat the transmitter, the scanning delays at the subscriber station willoperate in the same manner and in synchronism with the scanning delaysat the transmitter.

It will now be understood that the coder system at the subscribersstation operates in substantially the same manner as the coder system atthe transmitting station and that it comprises the same componentsexcept that it does not contain frequency divider 30 and double-pulsecoder 32 but in lieu thereof it contains reset pulse separator 71.Component 71 is shown in schematic form in FIGURE 7 and will also befound in Waveforms, by Chance, Hughes, MacNichol, Sayre and Williams,Radiation Laboratory Series, vol. 19, p. 367, McGraw-Hill Book Company,1949. Except for the biasing arrangement, the circuit of FIGURE 7 isidentical with that of the double-pulse coder shown in FIGURE 6 whichwas previously described in detail. The single dual-triode shown inFIGURE 7, together with its associated delay line, accepts a coded resetor cycling pulse consisting of two closely and accurately spaced pulsesgenerated by the reset pulse coder at the transmitter. The reset pulseseparator rejects pairs of pulses except when their spacing correspondsexactly with the delay introduced by the delay line in the separator.The coded cycling or reset pulse is separated from the compositesynchronizing pulse input and passes to cycler 31 shown in block form inFIGURE 2 or as shown in greater detail in FIGURE 8.

The advantages of the present system will now be apparent to personsskilled in the art. The present system provides a subscriber televisionsystem in which no mechanically movable elements are employed and inwhich all necessary signals are transmitted in the same envelope as inconventional television.

If desired, instead of using the diode binary coder unit as describedabove, a magnetic binary coder unit as shown in FIGURES 8 or 9 may beemployed as an alternate device for deriving the coded pulse sequencesto serve the purpose of this invention at the transmitter and at thesubscribers receivers.

The present magnetic coder unit is derived from a magnetic device whoseoperation is disclosed in a paper entitled Static Magnetic Storage andDelay Line by An Wang and Way Dong Woo, Journal of Applied Physics,January 1950, pp. 49-54, inclusive, and the same is embodied herewithand made a part of the present specification by reference.

For simplicity, the particular arrangement illustrated in the drawingsand to be described generates successive groups of 8 binary digitsrepresented by ON or OFF pulses, but it is clear that the coder unit mayreadily be enlarged or extended so as to produce groups of any requirednumber of binary digits with optional switch arrangements for setting upthe scanning code in correspondence with a key code for the switches.

Referring to FIGURE 8, the coder unit includes 16 or any other desirableeven number of magnetic toroids 40. To satisfy the principle ofoperation of the device as shown and described by the authors Wang andWoo, each toroid has -rst a winding 42, the windings of the odd numberedtoroids being connected together in series and to the cathode circuit ofthe driving tube here shown as the thyratron V5, whereas windings 42 ofthe even numbered toroids are similarly connected together and to thecathode circuit of the other driving tube also shown as a thyratron V6.Each pair of adjacent toroids also has a pair of connected windings 43which are connected together in the manner shown by means of rectifyingdiodes 44 in series between the windings and rectifying diodes 45 acrossthe windings 43.

The coder unit as thus far described corresponds to the device disclosedand described by the authors Wang and Woo. When in this system thetoroids are magnetized to saturation, alternate delivery of pulses bytubes V5 and V6 will produce at the output end of the system, mainly atline 46, a group of ON or OFF pulses depending upon the direction ofmagnetization of the several toroids. In its present adaptation, andparticularly for the purpose of the present invention, each toroid isadditionally provided with a winding 48, as shown in FIG. 8, these beingconnected in series through double-pole, double-throw toggle switches50, which are connected to the odd-numbered cores, and thence to thecathode circuit of thyratron tube V2. Thyratron tube V2 and itsimmediately associated elements constitute the cycler shown at 31 in theblock diagram of the transmitter system shown in FIG. l. The coder unitdriver shown at 29 in the block diagram of FIG. 1 comprises thescale-of-two tubes V7a and V7b together with the previously referred tothyratron tubes V5 and V6. The negative Vertical synchronizing pulsesare delivered to therminal A of the scale-of-two stage and thethyratrons V5 and V6 are consequently energized alternately and deliverpulses alternately to the odd and even-numbered windings 42 of themagnetic binary coder unit.

Input terminal A of the 8-digit binary coder receives a sequence ofregularly spaced pulses, say at a rate of 60 per second. At outputterminal 46 pulses will appear at a regular 30 cycle rate only if the 8toggle switches are set in the up position. If we consider a timeinterval corresponding to 16 consecutive input pulses and number theswitches 1 to 8, the setting of any toggle switch in the down positionwill remove the correspondingly numbered pulse of the sequence of 8 fromthe output. Since there are two possible ways in which each of the 8switches may be set, there are 28 or 256 distinct sequences of pulseswhich may be set up in consecutive groups of 8 equally spaced timeintervals of 1/30 second, provided the special cases of continuouspulses with all switches up and no pulses with all switches down areincluded. As indicated above, the arrangement may readily be extended byadding more small saturable reactors and switches. Considered in groupsof n equally spaced time intervals, there would then be 2n differentpulse sequences available. In a practicable example n might be equal to20 and 2n then would equal 1,048,576.

The magnetic binary coder unit is shown in FIG. 8 with 16 smallsaturable reactors and 8 associated doublepole, double-throw reversingtoggle switches, together with the required tubes V5, V6, and V7 fordriving the reactors. The coder unit is only one component of thesubscriptiontype television system shown in FIGURES l and 2. Theremainder of the circuit is identical with that used with the diodebinary coder previously described.

As shown in the schematic of FIG. 8 the windings 48 of the reactors inthe coder unit are connected in series with a reversing switch 50`provided for each odd-numbered reactor so that the core of the latterreactors can be polarized in the desired direction. The magneticmaterial used in these reactors saturates very rapidly as themagnetizing current is increased, and has very high retentivity and anapproximately square hysteresis loop. This means that once the core ismagnetized in a particular polarity, further pulses of magnetizingcurrent in the same direction will not change the ux and no inducedVoltage will appear across the windings. However, a pulse of current ofsufficient amplitude in the reverse direction will fflip theAmagnetization over to the opposite saturated polarity and result in arelatively large pulse of induced voltage across the reactor windings.

We shall assume that uniformly spaced pulses at a 60 cycle rate areapplied to the circuit of FIG. 8 at A, and that the reset pulses from V2occur coincident with every 16th of the 60 -cycle input pulses.

There are 256 different up-down positions in which the switches can bemounted, but in this example the switches will be arranged so that allof the reactor cores are magnetized in the same saturated polarity bythe reset or cycling pulse when all of the switches are down, or in theopposite saturated polarity when all of the switches are up.

The regular input pulses at A are applied to scale-oftwo stage Via-V7bwhich alternately triggers the miniature thyratrons V5 and V6. Theodd-numbered reactor have windings connected in series with the cathodeof V5 and ground, and the even-numbered reactors have windings connectedin series with the cathode of V6 and ground. As the input pulsesprogress, alternate cores in the c'hain are energized by the alternatering of thyratrons V5 and V6. The polarities of the windings and theinter-connections are such that these advancing pulses applied towindings 42 of the reactors cause a pulse to be passed from anyodd-numbered core which has its toggle switch in the up positionsuccessively to cores to the right, through the chain of cores andthence to the output terminal 46. The sequence of 8 binary digits willcontinue with the same pattern for successive groups of 16 input pulsesas long as the switch positions are not changed. When all of theswitches are up, pulses will appear continuously at the 3() cycle rateat the terminal 46. If any toggle switch is turned down the pulse fromthat particular core will be removed from the sequence. Finally, if allswitches are down, no pulses will appear at 46.

We now have a device for coding a uniform sequence of input pulses intoa sequence `of groups of binary digits represented by successive groupsof ON and OFF pulses.

The purpose of the rectifier elements 44 and 45, which may be germaniumdiodes, selenium elements, or other rectifying elements, is to insurethat the advancing pulses move digits only in the forward direction, andonly one core at a time in this direction.

A more detailed explanation of the operation of this magnetic circuit isgiven in the reference cited above.

One feature of the coding system is the code system synchronizing pulseor reset pulse. A source of these pulses is available at the transmitterand at all subscribers stations. This reset pulse is preferablygenerated from the vertical synchronizing pulse at the transmitter andtransmitted in the same envelope with the video and conventionalsynchronizing pulses. These reset pulses perform the same services inthe transmitter and in all receivers. Broadly, the reset pulses maintainall coder units energized in synchronism in a fashion identical withthat described above in connection with the diode binary coder.

In the preferred system reset pulses are generated at the transmitter,by frequency divider 30. The frequency of the reset pulse is determinedby the number of ON or OFF pulses in each code group generated by coderunit 28, it being desirable to have one reset pulse for each group ofcode pulses. Thus when the coder unit generates an eight pulse code, itis desirable to have one reset pulse for every eight code digits. Thecode digits in the magnetic coder being synchronized with every othervertical synchronizing pulse, there will be generated by the frequencydivider one reset pulse for every sixteen vertical synchronizing pulses.Such pulse-frequency dividers are common in the art and will not bedescribed in detail here.

The reset pulses are delivered to cycler 31, which, as

shown in FIG. 8 consists essentially of thyratron tube V2 and is in turnconnected to code input windings 48. Thus it will now be understood thatfor the first, seventeenth, etc., vertical synchronizing pulse a resetpulse passes through all windings 48 and, depending upon the directionof the winding of each odd-numbered core and the position of itsassociated switch 50, these magnetic cores will be polarized in onedirection or another. The cycler as represented by thyratron V2 alsodelivers each reset pulse to tube V'7a of the scale-of-two driver stageand to V4a of the electronic switch. The reset pulses serve tosynchronize the binary coder unit and the control mechanism orelectronic switch with the corresponding units when properly coded atthe subscribers television receiver. As thus far described, coder unit28 shown in schematic form in FIG. 8 may be set to deliver apredetermined code group of 8 ON or OFF pulses, the unit being triggeredby the vertical synchronizing pulses and being controlled by the resetor code systeml synchronizing pulses which are delivered by cycler 31 tocode input windings 48. The reset pulses are also delivered to coderunit driver 29 and to electronic switch or control mechanism 26 for thepurpose of synchronization.

The groups of ON or OFF pulses constitute a jittering or phasing codefor abnormal scanning of the picture converter 10.

As explained above, the output from the magnetic binary coder consistsof a repetitive group of binary digits, each group consisting of asequence of 8 equally spaced ON or OFF pulses depending upon how the 8switches are set. This sequence of pulses triggers, in an irregular butadjustable fashion, the 2-position electronic switch shown in FIG. 4.Each successive pulse causes V4a and V4b to conduct alternately and thisaction alternately turns on the switch tubes V3a and V3b. When either ofthese switch tubes conducts, it effectively grounds the diode which isconnected to its plate and prevents the pulse from the delay line frompassing that diode to output terminal E. The electronic switch thereforealternately connects the terminals D0 and D1 of the delay line to theoutput terminal E. The horizontal synchronizing pulses at thetransmitter are fed to the delay line and the pulses appearing at theterminal D0 are undelayed, whereas those appearing at the terminal D1are delayed by a fixed amount. The pulses appearing at output terminal Eare therefore jittered in time at an irregular rate established by thesetting of the coder switches at the transmitter. These jittered pulsesare passed to the sweep generating circuit in the camera at thetransmitter.

The above described action of the magnetic binary coder and associatedelectronic switch and delay line is similar to the action of the diodebinary coder and auxiliary apparatus as previously described. The codingdiffers somewhat with the magnetic coder as shown in FIG. 8 as comparedwith the coding derived with the diode coder of FIG. 3. In the lattercase the code consisted of repeating groups of 8 binary digits, thedigits occurring at a rate of 60 per second, whereas with the magneticcoder 8 binary digits occur at a rate of 30 per second.

In an alternate connection of the magnetic reactors of the magneticbinary coder as shown in FIG. 9, the S-digit binary code groups areidentical with those generated by the diode binary coder of FIG. 3 whichwas previously described.

In the circuit of FIG. 9 the sixteen magnetic reactors are operated intwo groups of eight reactors switched in parallel. The interconnectionsare such that when the sequence of vertical synchronizing pulses at arate of 60 per second are applied to input A of the scale-of-two driverthere are derived at output terminal 46 repeated groups of eight binarydigits represented by ON or OFF pulses occurring at a rate of 60 digitsper second. With the parallel form of the magnetic coder as shown inFIG. 9, reset pulse generator 30 (at the transmitter) is designed togenerate one pulse for every eight vertical synchronizing pulses. Theseparated reset pulse at the subscribers receiver is applied to inputterminalB of cycler 31 (V2) which in turn delivers reset pulses to thescaleof-two driver to input windings 48 of the magnetic reactors, and toelectronic switch 26 (V4a, FIG. 4).

The binary-coded pulses from the output terminal 46 of the magneticbinary coder of FIG. 9 are used, as with the previously described binarycoders, to control electronic switch 26 to effect abnormal scanning orother abnormal switching as previously discussed. At the subscribersreceiver the same magnetic binary coder unit may be used to properlyphase the switching functions in the receiver with those at thetransmitter in order to receive undistorted images on the screen.

By varying the direction of winding of code input or energizing windings48 or by varying the order of switches 50, the number of individualcoder units becomes enormous and it becomes practically impossible for agroup of friends to rewire the coder units so that they may all operateon the same key code.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within the truespirit and scope of the invention.

We claim:

1. A subscription television system comprising: a secrecy device havinga plurality of distinct operating conditions each of which establishes adilerent operating mode in said system; a control mechanism coupled tosaid secrecy device and having a plurality of stable operatingconditions, each etective to establish said secrecy device in anassigned one of its aforesaid operating conditions; a plurality of inputcircuits for said control mechanism, each selectively energizable tooperate said control mechanism to a different assigned one of itsaforesaid operating conditions; a first signal source including anadjustable code-determining switching apparatus for developing a firstseries of code signal pulses having an irregular time spacing determinedat least in part by the instantaneous adjustment of saidcode-determining switching apparatus; a second signal source fordeveloping a second series of code signal pulses, said first and secondseries of pulses collectively representing a code schedule; meanscoupled to said first signal source and to one of said input circuitsfor utilizing the code signal pulses of said iirst series to selectivelyenergize said one input circuit; and means coupled to said second signalsource and to another one of said input circuits for utilizing the codesignal pulses of said second series to selectively energize said otherinput circuit whereby said control mechanism is operated between itsaforesaid operating conditions in accordance with said code schedule.

2. A subscription television system comprising: a secrecy device havinga plurality of distinct operating conditions each of which establishes adifferent operating mode in said system; a bi-stable control mechanismcoupled to said secrecy device and having two stable operatingconditions, each elfective to establish said secrecy device in anassigned one of its aforesaid operating conditions; a rst input circuitfor said control mechanism energizable to operate said control mechanismto a predetermined one of its two operating conditions; a second inputcircuit for said control mechanism energizable to operate said controlmechanism to the other one of its two operating conditions; a firstsignal source including an adjustable code-determining switchingapparatus for developing a first series of code signal pulses having anirregular time spacing determined at least in part by the instantaneousadjustment of said codedetermining switching apparatus; a second signalsource for developing a second series of code signal pulses, said firstand second series of pulses collectively representing a code schedule;means coupled to said first signal source and to both said iirst andsecond input circuits for utilizing the code signal pulses of said rstseries to effect operation of said control mechanism from itsinstantaneous condition, whichever one that may be, to its alteratecondition; and means coupled to said second signal source and to saidsecond input circuit for utilizing the code signal pulses of said secondseries to effect operation of said control mechanism to said otheroperating condition if said control mechanism is not already establishedin that operating condition.

3. A subscription television system for receiving a scrambled picturetransmission, wherein picture signals are transmitted in one of aplurality of different modes during different time periods which occurat a rate sufficient to render an unauthorized receiver displayunintelligible and wherein signals are transmitted representing theoperation of commutation means at the transmitting means comprising:means ,for resolving the different modes of said picture signals, meansincluding commutation means coupled to the resolving means fordetermining from time to time the mode resolved in the resolving means,means for detecting the transmitted signals and coupled with thecommutation means for maintaining synchronization of the receivercommutation means with corresponding commutation means at thetransmitting means, and changeable matrix means connected between themode resolution means and the receiver commutation means for determiningthe mode to be resolved for given states of the commutation means.

References Cited bythe Examiner UNITED STATES PATENTS 2,557,581 6/1951Triman 340-147 2,573,349 10/1951 Miller et al 340-147 2,594,731 4/1952Connolly 340-1741 X 2,816,156 6/1957 Pawley et al l78-5.l 2,833,85012/1957 Bartelink 178-5.1

NEIL C. READ, Primary Examiner.

EVERETT R. REYNOLDS, STEPHEN W. CAPELLI,

Examiners.

3. A SUBCRIPTION TELEVISION, SYSTEM FOR RECEIVING A SCRAMBLE PICTURETRANSMISSION, WHEREIN PICTURE SIGNALS ARE TRANSMITTED IN ONE OF APLURALITY OF DIFFERENT MODES DURING DIFFERENT TIME PERIODS WHICH OCCURAT A RATE SUFFCIENT TO RENDER AN UNAUTHORIZED RECEIVE DISPLAYUNINTELLIGIBLE AND WHEREIN SIGNALS ARE TRANSMITTED REPRESENTING THEOPERATION OF COMMUTATION MEANS AT THE TRANSMITTING MEANS COMPRISING:MEANS FOR RESOLVING THE DIFFERENT MODES OF SAID PICTURE SIGNALS, MEANSINCLUDING COMMUTATION MEANS COUPLED TO THE RESOLVING MEANS FORDETERMINING FROM TIME TO TIME THE MODE RESOLVED IN THE RESOLVING MEANS,MEANS FOR DETECTING THE TRANSMITTED SIGNALS AND COUPLED WITH THECOMMUTATION MEANS FOR MAINTAINING SYNCHRONIZATION OF THE RECEIVERCOMMUTATION MEANS WITH CORRESPONDING COMMULATION MEANS AT THETRANSMITTING MEANS, AND CHANGEABLE MATRIX MEANS CONNECTED BETWEEN THEMODE RESOLUTION MEANS AND THE RECEIVER COMMUTATION MEANS FOR DETERMININGTHE MODE TO BE RESOLVED FOR GIVEN STATES OF THE COMMUTATION MEANS.